Ultra-high-frequency tuner



Dec. 11, 1956 J. F. WlLCOX ULTRA-HIGH-FREQUENCY TUNER Filed Oct. 17. 1951 Inventor:

m M N W F t s A e United States Patent ULTRA-HGH-FREQUENCY T NE James F. Wilcox, Syracuse, N. Y'., assignor to General Electric Company, a corporation of New York App i a ion Oct ber 1 l95 r a N ,6

5' Claims, (Cl. 333-82) My invention relates generally to ultrahigh-frequency apparatus, and more particularly to tuning-circuit arrangements operable over a relatively wide band of ultrahigh-frequency values.

Heretofore, tuning-circuit, arrangements have been clescribed' for use with ultra-high-frequency apparatus, but such arrangements have either been excessively large and bulky and costly to produce, or such arrangements have comprised certain structural featuresv such as sliding conductive contacts. that require frequent adjustment and replacement. Other arrangements that have been described comprise lumped-constant circuit elements which are not very feasible in the desired frequency range. It is, therefore, a primary object of this invention generally to, improve the art ofultra-high-frequency tuning arrangements.

Another object, is to provide such tuning arrangements that are, free from sliding conductive, connections and relatively simple in construction and economical to produce.

Still another object is to provide novel and improved tuning circuit, arrangements operable over relatively wide ranges of frequency values in the ultrahigh-frequency band.

Another object is to provide an adjustable tuning circuit including as elements thereof a plurality of sections of resonant transmission line having adjustable, reactive coupling therebetween.

Yet another object is to provide such an adjustable filter that is characterized in that a predetermined bandoffrequencies is readily passed by the filter, the cut off at one end of the pass band being relatively abrupt.

In accomplishing the foregoing objects, I eliminate the undesirable sliding conductive connections characteristic of'conventional types of high-frequency tuners by employing a resonant section of transmission line having reactive means of the distributed constant type for varying the characteristic impedance of the transmission line. In accordance with one aspect of this invention, the transmission line isconstructed as a non-parallel pair of spaced conductors connected at one end to a reactive circuit to be tuned, and having at the other end, adjustable means for varying the characteristic impedance of the line,

In accordance with another aspect of this invention, the transmission line comprises a pair of parallel-wire or rod conductors connectible at one end to a reactive circuit to be tuned and having adjustable means at the other end for varying the characteristic impedance of the line.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In-the drawing, Fig. l is a side elevational view of one embodiment of my invention; Fig. 2 is a side view of the apparatus shown in Fig. 1; Figs. 3 and 4 are schematic diagrams useful in explaining the operation of the apparatus illustrated in Fig. 1-; Figs. 5-8 are plan-views illustrative f other embodiments of the invention; and Fig. 9 is a perspective view ofa further. modification of the invention. Referring to Figs. 1 and 2 of the drawing, an adjust- 2,774,045 l ateiited Dec. 11, 1956 ICC ab e tune nstr ct r n danc w h he p e nvention is shown, comprising a section of non-uniform transmission line 11 having a ground plate 13, which may be a flat strip of brass or other suitable conductive material, disposed in cooperative relation to an arcuate'strip 15, of spring material. The plate 13 and strip 15 are spaced from each other and secured, together by means of a spacer block 17 of any suitable insulation material, the connection of the conductors 13, 15 to the block 17 being effected in any conventional manner. Input terminals 19 are provided at the end of transmission line 11 adjacent the block 17 for connection to a circuit to be tuned or resonated. To vary the characteristic impedance of the line 11, the spacing between the plate 13 and strip 15 is adjustable by altering the curvature of strip 15, as by an insulating screw 21 that is suitably supported in an insulating frame 23.

' An approximate theory of operation of the abovedescribed tuner circuit can be obtained by consideration of the lumpedparameter equivalent circuit shown in Fig. 3, taken in connection with the diagram of Fig. 4, which is illustrative of a distributed-parameter circuit roughly equivalent thereto.

In Fig. 3-, the capacitance C represents the effective capacitance of an apparatus which is desired to be tuned by the apparatus of the present invention and the resist ance R represents the load resistance. The tuning reactance is represented by the reactance Z1 equivalent to the reactance of the non-uniform line 13, 15 of- Figs. 1 and 2. The arrangement is, therefore, quite similar to that of a band-pass filter approximating the non-uniform transmission line of Fig. 4 of which the input impedance Z1, by well-known transmission line theory, may readily be shown to be:

1+ o2 3 1 Got 1 2 (1) where Z0; is the characteristic impedance of the first sec? tion of transmission line shown having a length 11, 202 is the characteristic impedance of the second section of transmission line having a length 12 and p is the phase constant of the line. In the case under consideration,

The expression for Z1 in Equation 3 yields a filter characteristic corresponding to that of a band-pass circuit and similar to that of a lumped tuned circuitfor the proper line parameters. An illustrative calculation made with the following values:

C=5 mmf.

Z 1=50 ohms Z02: ohms discloses that the circuit tunes to 700 megacycles per second with a band width, at 70% of the voltage, of 22 megacycles per second. The characteristic of this circuit corresponds to that of a single parallel-tuned circuit with lumped constants.

By suitably changing theline'parameters, wider tuning may be obtained, and it can be shown that a bandwidth of tuning equal to 25 megacycles-per second at a resonant frequency of 1230 megacycles per second can be obtained. It willlbe understood that the foregoing calculations are merely exemplary and are not to be considered as limitations' of the scope of the invention.

By a suitable choice of values for It and l: for the ratio Zo2/Zo1, Z1 can be made zero at a desired frequency value. Accordingly, the filter characteristic shows an abrupt cut ofi or rejection region corresponding to substantially infinite attenuation. For example, in the ,case where the circuittunes acapacitative' element, such a region can be shown to occur at a frequency substantially equal to 60 megacycles per second below the tuning frequency of 1230 megacycles per second. It will thus be seen that such a characteristic is extremely useful for rejecting undesired image signals commonly encountered in the reception of radioafrequency signals. The rejection or cut-01f frequency can be made to track with the tuning of the pass band, thus rendering the filter circuit extremely useful as a tuner for television receivers.

Where the circuit element is employed to tune an inductive element instead of a capacitative element, the rejection region occurs on the high-frequency side. of the pass band.

In practice, it is a capacitance that is commonly sought to be tuned. Thus, if the rejection region is desired on the high-frequency side, one needs only to connect an inductive element across the capacitance so that the net reactance presented to the circuit is inductive over the desired tuning range;

Fig. 5 illustrates the principle of the present invention as embodied to an open-circuited transmission line having a flared portion along part of its length. Thus, a transmission line 30 is shown comprising a parallel-wire section 32 and a non-uniform wire section 34 directly coupled thereto. For altering the characteristic impedance of the transmission line 30, thereby to vary the resonant frequency of the filter, a wedge-shaped conductive slug 36 is adjustably positionable in the space between the non-uniform wire portion 34 as by a rack and pinion drive 38 actuating an insulating rod 39. To avoid direct or sliding contact between the slug 36 and the flared portion 34, a thin solid dielectric coating 40 may be aflixed to the surfaces of the slug 36 adjacent the portion 34. The circuit to be tuned is connected at terminals 41 provided at the end of the line section 30 remote from the tuning slug 36.-

Fig. 6 illustrates a similar arrangement for a shortcircuited line 42 which, as shown, comprises a bent section of transmission line which may be formed as a V-shape member, or in any other desired configuration. A conformable triangular slug 46 is movable in and out of the V portion to vary the characteristic impedance thereof. Input terminals 47 are provided at the free ends of the transmission line section for connection to an external circuit. If desired,.solid dielectric coatings may be applied as described hereinabove in connection with the embodiment of Fig. 5.

Figs. 7 and 8 illustrate further embodiments of the invention, in which the slugs 36 or 46, shown in Figs. 5 and 6, are replaced by a conductive rod or tube, as at 48 and 52, bent to form a short-circuited line section having inwardly bent portions 48' and 52', respectively, which are interconnected by cross members 48" and 52", respectively. Such short circuited line sections may be adjustably movable into the space between the flared portions 34 of the transmission line 30 by means similar to the rack and pinion device 38 shown in Fig. 5. In Fig. I

8,.the arrangement is quite similar to that shown in Fig. 7; with the exception that an adjustable impedance element 50'of any suitable character and magnitude may be connected into the movable short-circuited line section 52. The impedance 50 affords an additional parameter thatcan be varied for further control'of the filter characteristics'.

Fig. 9 illustrates a modification of the basic principles of the present invention as embodied in a parallel-wire transmission line. As shown, an open-circuited parallelwire transmission line section 51 is provided consisting of a pair of flat strips 54, 56 of suitable conductive material, which are suitably fastened to a support 58 in any conventional manner. For a major portion of their length, the strips 54, 56 are spaced from the support 58 as by downwardly-curved terminal parts 59, 62, thus defining a space between the strips 54, 56 and the support 58 into which a short-circuited line section 60 may he slidably positioned and in spaced relation to the overlying strips 54, 56. The short-circuited line section 60 consists of a pair of conductive strips 61, 63, of substantially the same size and shape as strips 54, 56 of the open-circuited line. A shorting bar 65 interconnects strips 61, 63 and is provided with a pair of downwardly projecting studs 67,

69 which ride in associated slots 71, 73 in the support 58. t

The reactive coupling between the openand short-circuited line sections 51, 60 is readily varied in accordance with the degree of overlapping of the line sections 51 and 60. With large coupling, the lines sections 51 and 60 can be dimensioned to cooperate to act like a shortedquarter wave line. As the coupling is decreased, there is a gradual transition from the quarter-wave line mode to a half-wave line mode.

If desired, a strip of solid dielectric material 64 may be disposed between the adjacent surfaces of the strips 54, 61 and 56, 63 to alter the magnitude of the reactive coupling. A dielectric block 68 is provided for securing the short-circuited line 60 in any desired position with respect to the open-circuited line 51. To this end, an adjusting screw '70 passes through suitable aligned openings in the block 68 and the insulation strip 64, and into a threaded portion (not shown) in the support 58. Connection to a circuit to be tuned may be made at the ter minals 72, 74..

While I have shown and described various specific o embodiments of my invention, and certain modifications thereof, it will, of course, be understood by those skilled in the art that other modifications may be made without departing from the principles of the invention. I, there-' fore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is: p y

1. An ultra-high-frequency filter circuit comprising a first section of two-conductor transmission line having a parallel conductor part and a flared conductor part connected thereto, a second section of two-conductor transmission line of which the conductors are conformably disposed relative said flared part, said second-section being movable relative said first section to define therewith a filter having variable tuned-circuit characteristics, and variable reactance means connecting corresponding ends of the conductors of said second section remote from said first section thereby to affect alterations in the tunedcircuit characteristics of said filter in accordance with the value of the reactance of said variable reactance means. 2. An ultrahigh-frequency apparatus embodied in a non-uniformly spaced transmission line comprising a section of parallel-conductor transmission line having a flared portion and a conductive member positioned in said flared portion, said transmission line and said conductive member being movable relative to one another to vary the char.- a'cteristic impedance of said line, and said conductive member comprising a short circuited section of two-conductor transmission line having portions conformable with said flared portion. s

3. An ultra-high-frequency apparatus embodied in a non-uniformly spaced transmission line comprising a section of parallel-conductor transmission line having a flared portion, a conductive member movable in said flared portion to vary the characteristic impedance of saidline, said conductive member comprising a short-circuited section of two-conductor transmission line having portions conformable with said flared portion, and a reactive load included in said short-circuit line. section.

4. An ultrahigh-frequency apparatus embodied in a non-uniformly spaced transmission line having a flared portion, a conductive member conformable to and positioned in said flared portion, said conductive member and said flared portion being movable relative to one another, said conductive member being reactively coupled to said flared portion to vary the characteristic impedance of said line.

5. The apparatus as in claim 4 wherein said conductive member is a Wedge-shaped slug.

References Cited in the file of this patent UNITED STATES PATENTS 2,246,928 Schick June 24, 1941 6 Keister July 1, 1941 Roberts Feb. 27, 1945 Alford Feb. 26, 1946 Leeds Aug. 6, 1946 Harvey Dec. 3, 1946 Malling Feb. 4, 1947 Gurewitsch Feb. 3, 1948 Rado June 19, 1951 Martenot Jan. 8, 1952 Murakarni June 24, 1952 

